Acoustic damping in Li2O–2B2O3 glass observed by inelastic X-ray and optical Brillouin scattering

Abstract The dynamic structure factor of lithium-diborate glass has been measured at several values of the momentum transfer Q using high resolution inelastic X-ray scattering. Much attention has been devoted to the low- Q -range, below the observed Ioffe–Regel crossover q IR ≃ 2.1 nm −1 . We find that below q IR , the linewidth of longitudinal acoustic waves increases with a high power of either Q , or of the frequency Ω , up to the crossover frequency Ω IR ≃ 9 meV that nearly coincides with the center of the boson peak. This new finding strongly supports the view that resonance and hybridization of acoustic waves with a distribution of rather local low frequency modes forming the boson peak is responsible for the end of acoustic branches in strong covalent glasses. Further, we present high resolution Brillouin light-scattering data obtained at much lower frequencies on the same sample. These clearly rule out a simple Ω 2 -dependence of the acoustic damping over the entire frequency range.